In milling, the performance of the milling is largely determined by the combined natural frequencies of the assembled system, which includes a machine, a rotatable spindle or holder mounted to the machine, and a milling cutter body that is connected to the spindle and has one or more cutting edges. The cutting edges may be integrated with the milling cutter body or the milling cutter body is provided with one or more replaceable milling inserts each one of which is provided with one or more cutting edges. Elongate milling cutter bodies, in particular when mounting with a great protrusion length, have a tendency to cause a poor and irregular finish of the surface in the milled material, caused by so-called chatter, which may appear as waves on the milled surface of the workpiece.
For a specific spindle speed, including, for example, the number of revolutions per time unit of the spindle, there is a critical axial cutting depth and in case of cutting depths that are greater than the critical axial cutting depth, too great vibrations arise to be able to carry out a stable milling operation. If the speed of the spindle is changed, the critical axial cutting depth will change. Thus, it is important to select a combination of axial cutting depth and spindle speed where stability problems are avoided. However, it is not always possible to change the spindle speed to avoid stability problems, which may at least be due to speed control limitations in the machine and/or because increased cutting speed may cause higher temperature in the cutting zone, which in turn results in faster tool wear.
In prior art, there are several solutions that try to solve the problem of chatter vibrations and stability problems in cutting operations such as drilling, turning and milling.
U.S. Pat. No. 5,700,116 discloses a damping system to damp vibrations that are generated during, for example, milling, wherein an elongate tool body, to which milling inserts are mounted, is provided with an axial hole in which a damper mass is arranged. The damper mass is suspended by means of elastic O-rings, and the tuning of the damping system is provided by altering the pressure on the O-rings.
U.S. Pat. No. 3,447,402 discloses a system for drilling comprising a drill body provided with an axial central hole in which a damper mass is suspended by use of ring-shaped, elastic elements, wherein the damper mass is intended to vibrate to damp the vibrations of the system.
U.S. Pat. No. 3,774,730 discloses a drill body provided with a cavity in which a damper mass is suspended by resilient O-rings to allow the displacement of the damper mass in relation to the drill body damp vibrations in the drill body.
U.S. Pat. No. 3,838,936 discloses a damper device for a drill body comprising a damper mass contained in an axial hole arranged in the drill body, the damper mass being suspended by resilient rubber rings to damp undesired vibrations. The damping is adjusted by the pressure on the rubber rings being adjusted.
U.S. Pat. No. 5,957,016 discloses a method for controlling the chatter vibrations in a cutting tool system, wherein the natural frequency of the system is modulated by piezo-electric materials, electrorheological fluids, fields of sinusoidal shape and/or signals of square-wave shape.
U.S. Pat. No. 4,047,469 discloses a method to damp chatter vibrations in, for example, a milling cutter by applying a rotating damper mass in contact with the cutting tool or the spindle and continuously displacing the damper mass along the cutting tool or the spindle to shift the contact pressure and thereby change the natural frequency of the system to suppress the chatter vibrations.
US 2006/0291973 discloses a system to reduce the vibrations in a cutting tool, wherein the body on which the cutting tool is mounted is provided with an axial cavity in which a damper mass is displaceably suspended by elastic rings.
WO 2006/010093 discloses a method for damping chatter vibrations in tool systems, wherein calibration weights are attached to a tool holder in the system to adjust the natural frequency of the holder.
U.S. Pat. No. 3,559,512 discloses a system to damp vibrations during drilling, wherein the drill body has a central axial hole in which a set of damper masses are suspended by ring-shaped, elastic damping elements.
U.S. Pat. No. 3,938,626 discloses a structure to damp vibrations, wherein a drill body has an axial cavity in which a set of damper masses are displaceably suspended by a bar extending axially in the cavity.
U.S. Pat. No. 5,170,103 discloses a device to reduce chatter vibrations in cutting tool systems, wherein a body mounted on a holder is provided with an axial cavity, and wherein a damper mass arranged in the cavity is displaceably suspended by an elastic element.
However, the methods and apparatuses mentioned above do not provide sufficiently flexible and efficient solutions to efficiently overcome stability problems and vibration problems in milling.